Are you struggling between templates & campaigns?
A template is created once - it contains all your styles for the future campaigns. There is no need to create a new one for each campaign.
To create a campaign in Mailchimp, click on the Create Campaign button, and follow the set-up process. Step 3 will be to select the template. Click on 'Saved Templates' and select 'Newsletter' or whatever your template is called. And then proceed with entering your content. No need to alter or enter any styles - all done using your template.
If you struggle with Mailchimp, we can help you get the best out of this product.